1. Field of the Invention
This invention relates in general to any application of fluid control valves where high reliability of operation is essential. Such applications exist in a number of industries. In particular this invention relates to emergency shut down systems used, for example, in the processing industries. Typically oil and gas plants will have pneumatically controlled emergency valves within their systems. In the event of a potential hazard the emergency valves will operate to either close thus isolating the plant, or open thus providing a bypass to controlled fluids. In many instances, these emergency valves may remain in their operational position for a period of months or even years. Therefore a frequent problem with such valves is that they may fail to operate correctly in the event of an emergency because components have become seized or slow to response. This problem may lead to a hazardous situation. This invention relates to the automated testing of such valves with minimum impact on the normal operation of the plant to gain increased confidence that in the event of a potential hazard the valve will operate as intended.
2. Description of the Related Art
A number of products exist within the market that provide automated testing of valves, including emergency valves. Many of these are based on initiating the sequence to be adopted during a hazardous situation for a period of time that is long enough to determine that the valve is not seized and is free to operate correctly, but of a short enough period so that the valve does not fully operate and disturb the controlled process. Such automated test mechanisms are termed partial stroke testing within the field.
U.S. Pat. No. 6,089,269 teaches partially stroking an emergency valve based on a predetermined voltage off period. The '269 patent teaches initially turning the timers to a minimum and gradually increasing the voltage off period in order to avoid overshooting the desired valve position.
U.S. Pat. No. 6,920,409 describes a method of partial stroke testing based on a predetermined time interval. The method then compares data gathered from previous successful operations of the valve with data gathered during an automated test. Should the data differ between the initial test and the subsequent test in key aspects, the potential for failure of the valve would be identified.
The present invention describes a method for the detection of potential valve failure without the need for initial testing or initial test data.